The present invention relates to a method and a device for controlling a brake system.
A method and a device for controlling a brake system are known. For example, SAE Paper 960991 describes an electrohydraulic brake system in which a braking command input of the driver is derived from the actuation of the brake pedal by the driver. This input is converted into setpoint braking pressures for the individual wheel brakes, optionally taking into account other braking variables. The setpoint braking pressures are adjusted for each wheel by pressure closed-loop control circuits as a function of the prescribed setpoint pressure and the actual braking pressure as measured in the area of the wheel brake. In a hydraulic brake system of this type, an accumulator is provided which is charged by an electrically controllable pump for supplying pressure to the brake system. Since the functioning of this pressure supply is essential for the operational readiness of the electrohydraulic brake system, the correct function of the pressure supply must be monitored. In addition, provision must be made for measures which permit the driver to apply the brakes of the motor vehicle equipped with the brake system, even in the case of a failure of the pressure supply.
An object of the present invention is to provide measures by which the operativeness of the pressure supply of an electrohydraulic brake system can be reliably determined. In addition, measures are to be provided which assure reliable operation of the brake system even in the case of failure of the pressure supply of the electrohydraulic brake system.
A reliable operating procedure for monitoring the operativeness of the pressure supply of an electrohydraulic brake system is made available. In this context, the recognition of failure occurs very quickly and accurately as a result of the evaluation of gradients. It is not necessary to wait for a complete charging cycle of the pressure supply accumulator. It is particularly advantageous that various sources of failure can be isolated.
It is advantageous that, for the pressure change, setpoint values are formed in which the prevailing operating state of the pump is taken into account. This contributes to the accuracy, the speed, and the reliability of fault detection.
It is a further advantage that the monitoring of the operativeness of the pressure supply is limited to operating states in which the accumulator pressure is to be built up or maintained, so that it is not necessary (i.e., need not be observed) to monitor the correct accumulator level during a braking intervention (which is very unreliable and difficult), during which volume is removed from the accumulator.
In this context, monitoring the accumulator pressure takes place by means of sensing a preselected absolute minimal pressure PSY.
In addition, it is advantageous that in the event of a fault, as a result of switching to a purely hydraulic brake system, the braking of the motor vehicle equipped with the electrohydraulic brake system is assured.